Delta-metal
A gun-metal of great density and strength. Its composition is: copper 56, tin 1, zinc 41, iron 2. The wrought iron must be alloyed with the zinc in due proportion, and introduced as an iron-zinc alloy, in known proportions, in the customary manner. This alloy is similar to sterro-metal. An addition of lead (0.40 per cent) makes the composition more ductile and soft, and it is then called Tobin-bronze. Delta-metal can be forged or rolled at a dull-red heat, and may be drawn or hammered to a certain limit when cold. Castings made from this alloy are remarkable for their soundness, and have a tensile strength of from 40,000 to 50,000 pounds per square inch. See BRONZE. Density is the proportionate quantity of matter in bodies of a given magnitude; thus, if a body contain more matter than another, both being of the same bulk, the former is said to be more dense than the other. The quantity of matter is measured by the weight, and thus density and specific gravity come to be proportional to one another. Platina, which is about 21 times the weight of water, long passed for the densest body, but iridium is even more dense. Rare is opposed to dense; the rarest body known is hydrogen, which is about 14 1/2 times rarer than atmospheric air. Density of bodies is increased by cold and diminished by heat. See SPECIFIC GRAVITY.